1. Field
The present application relates generally to communication, and more specifically to filters.
2. Background
Wireless communication devices typically must transmit and receive signals in accordance with regulatory requirements that may vary between geographical regions. As a result, wireless communication devices must either be specifically manufactured for a particular region or must be able to operate in accordance with the regulatory requirements of multiple regions. Receivers and transmitters include signal filters for attenuating unwanted signals and noise. Transmitters within wireless communication devices typically include a transmission filter for filtering output going transmissions to minimize the amplitude of undesired signals while passing the desired signals. The transmission filter, therefore, should minimize attenuation of signals of the transmission band and maximize attenuation of signals outside the transmission band. In addition to transmission filters near the antenna, transmitters may include other interstage filters within the transmission lineup. Regulatory requirements often dictate the characteristics of the transmission filters due to the differences in the location and size of the frequency bands and the differences in restrictions in the location and authorized energy of transmitted signals and spurious emissions near or within the authorized frequency band. Conventional wireless communication devices either include a transmission filter that meets the requirements of a specific region or include multiple transmission filters. These conventional techniques are limited in that some devices may only operate in certain regions and that they result in increased manufacturing cost.
In addition, the operating environment changes as the device moves to different regions or to different locations within a region. In a sparsely populated location, interference and noise created by nearby devices may be minimal to a communication device. A filter with a frequency response that allows more energy to enter may be advantageous. When the communication device is exposed to a location with more devices and noise, it may be advantageous to utilize filters with narrower pass bands or with different center frequencies as compared to the filters used in a low noise environment. Conventional devices are limited in that either the devices are implemented with multiple filters or are implemented with filters that are not optimum for certain spectral conditions.
Therefore, there is need for a communication device with an adjustable filter.